﻿32 



GEOLOGICAL MEMOIRS. 



In concluding this notice, we must mention that in the succeeding 

 chapters, forming the 3rd and 4th Divisions of the work, several 

 points closely connected with geognosy occur ; especially on the com- 

 parison of the isothermal lines of the air with those of the earth, in 

 Chap, xiii., and on the connexion of vegetation with geological con- 

 ditions, in Chap. xxi. fT R T 1 



On Aptychus. By Leopold von Buch. 



[Leonhard u. Bronn's Neues Jahrb. f. Miner, u. s.w. 1850, 2 H. p. 244-245 ; 

 and Berlin. Monats-Ber. 1849, pp. 365-370.] 



In a lecture given before the Society of the Friends of Natural Hi- 

 story at Berlin, February 1849, Ewald has shown, that in the Sea- 

 phites binodosus, Roem., from the upper chalk of Haldem in West- 

 phalia, an Aptychus occurs, maintaining a certain position in the 

 cavity of the fossil, so that its medial line seems to be uniformly di- 

 rected under the dorsal line of the Scaphite (and consequently under 

 the siphon, which in the Ammonece generally extends somewhat into 

 the cavity), its broad end towards the mouth, and its convex side 

 towards the back of Scaphite. Subsequent to the Meeting of the Na- 

 tural Philosophers at Ratisbon, September 1849, some of the geolo- 

 gists went to Pappenheim and Aichstedt, where they found in the 

 collections of HH. Haberlein and Rettenbercher, and that of the 

 Duke of Leuchtenberg, some hundreds of Ammonites with enclosed 

 Aptychi, all of which, with some exceptions, had the above-mentioned 

 position. In perfectly preserved specimens their position was more 

 towards the hindermost wall of the cavity than towards the mouth. 

 Quenstedt, in his treatise on the fossil organic remains of Germany *, 

 likewise mentioned the regular position of these bodies at the back 

 of several Ammonites, but did not perceive the true direction of the 

 two ends. He has, however, explained that Aptychus possesses more 

 of a bone-like than of a shell-like texture, being composed of small 

 tubes ; that it possesses a shelly coating over the inward, concave 

 side only, and upon this side there are incremental stripes, for which 

 the folds, that certain groups of Aptychi have on their outside, must 

 not be mistaken. The folded species are pointed at their hindermost 

 end, but the smooth ones are round, and for the most part peculiar 

 to the macrocephali, and particularly to Am. inflatus, so plentiful in 

 the Upper Juraf. 



Burmeister has communicated the following opinion to the author 

 respecting the position of Aptychus as parts of the Ammonece. Most 

 of the Cephalopoda possess upon the back a calcareous plate*, which 

 in the Sepice is large, elliptical, and porous, and has upon one side a 

 firmer horn-like covering, which may be compared to the epidermis of 

 molluscs ; in the Loliginece, on the other hand, it is long and narrow, 

 and composed of two symmetrical, wedge-shaped halves. Apparently 



* Petrefactenkunde Deutschlands, i. 306 et seq. 



f Comp. Herm, v. Meyer Verh. der Leopold. Acad. xv. t. 58 ; Quenstedt, t. 22. 

 fig. a. 



